Polyamide resin composition

ABSTRACT

A polyamide resin composition contains a resin component containing at least a polyamide, a fatty acid metallic salt having from 10 to 50 carbon atoms, and an additive. The polyamide is obtained through melt polycondensation of a diamine component containing 70% by mol or more of m-xylylenediamine and a dicarboxylic acid component containing 70% by mol or more of an α,ω-linear aliphatic dicarboxylic acid. The additive is at least one compound selected from the group consisting of a diamide compound obtained from a fatty acid having from 8 to 30 carbon atoms and a diamine having from 2 to 10 carbon atoms, a diester compound obtained from a fatty acid having from 8 to 30 carbon atoms and a diol having from 2 to 10 carbon atoms, and a surfactant.

This application is a Continuation application of application Ser. No.12/302,335, filed Nov. 25, 2008, which is a National Stage Applicationfiled under 35 USC 371 of International (PCT) Application No.PCT/JP2007/061138, filed May 31, 2007. The contents of No. 12/302,335are herein incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a resin composition that contains apolyamide having a m-xylylene group and, depending on necessity, anotherpolyamide in the main chain thereof. More specifically, it relates to apolyamide resin composition that has favorable color tone, contains aless amount of gel, and can be subjected to melt extrusion processstably for a prolonged period of time.

BACKGROUND ART

A packaging material for foods, beverages and the like is demanded tohave such functions as strength, resistance to cracking, heat resistanceand the like for protecting the content from distribution, storage, suchas refrigeration and the like, and treatments, such as thermalsterilization and the like, and also demanded to have a wide variety offunctions, such as excellent transparency and the like for confirmingthe content. In recent years, furthermore, it is demanded to have oxygenbarrier property for preventing oxygen from invading from the exteriorfor suppressing foods from being oxidized, carbon dioxide barrierproperty and barrier property against various kinds of aromaticcomponents and the like.

A polyolefin, such as polyethylene, polypropylene and the like, apolyester, such as polyethylene terephthalate, and an aliphaticpolyamide, such as nylon 6, have been used widely as a packagingmaterial owing to good handleability and processability, and excellenttransparency and mechanical properties of a sheet or film obtainedtherefrom. However, it is poor in barrier property against a gaseoussubstance, such as oxygen and the like, and thus has such problems thatthe content is liable to suffer oxidation degradation, and aromaticcomponents and carbon dioxide are liable to penetrate therethrough toshorten the expiration period of the content.

A plastic container (such as a bottle) containing mainly a polyester,such as polyethylene terephthalate (PET) and the like, has been widelyused for tea, fruit beverages, carbonated beverages and the like. Theproportion of a small-size plastic bottle within the plastic containersis being increased year by year. The ratio of the surface area per unitvolume of the content is increased by decreasing the size of the bottle,and therefore, there is a tendency of shortening the expiration periodof the content when the size of the bottle is decreased. In recentyears, furthermore, beer, which is liable to receive effects of oxygenand light, is sold in a plastic bottle, and tea in a plastic bottle issold in a warmed state, which expand the application range of plasticcontainers. Under the circumstances, there is a demand of furtherenhancing the gas barrier property of a plastic container.

For enhancing the barrier property against a gaseous substance, such asoxygen, a film or the like formed by combining the aforementionedthermoplastic resins with a gas barrier resin, such as vinylidenechloride, an ethylene-vinyl alcohol copolymer, polyvinyl alcohol and thelike, is used. However, a film containing vinylidene chloride isexcellent in gas barrier property irrespective of the storageconditions, but has such a problem that it generates dioxin throughcombustion to contaminate the environments. An ethylene-vinyl alcoholcopolymer and polyvinyl alcohol are free of the before-mentioned problemof environmental contamination. However, a film formed therefromexhibits excellent gas barrier property under an environment of arelatively low temperature, but there is a tendency of decreasing thegas barrier property considerably in the case where the content to bekept has a high water activity or is kept under a high humidityenvironment, or the film is subjected to a thermal sterilizationtreatment after charging the content, whereby there may be a problem instorage stability of the content.

As a material excellent in gas barrier property, a polyamide containinga m-xylylene group in the main chain thereof obtained throughpolycondensation reaction of m-xylylenediamine and an aliphaticdicarboxylic acid, such as polyamide MXD6 obtained fromm-xylylenediamine and adipic acid, has been known. The m-xylylenediaminegroup-containing polyamide is used widely as engineering plastics owingto the high rigidity and excellent thermal property and moldingprocessability. It exhibits high barrier property against a gaseoussubstance, such as oxygen or carbon dioxide gas and the like, owing tothe m-xylylene group in the polymer main chain, and is used as a gasbarrier material for various packaging materials, such as a film, abottle, a sheet and the like, by combining with various resins, such aspolyethylene terephthalate and the like. However, upon molding them-xylylene group-containing polyamide into a film, a sheet, a bottle andthe like, air may be entrained upon melt processing to form bubbles, orappearance failure, such as silver stripes, uneven flows and the like,may occur unless the molding conditions, such as the screw shape, thetemperature, the back pressure and the like, are properly set. In thecase where a large amount of powder is contained in the pellets,particularly, there is a tendency that these phenomena may often occur,and there is a demand of improvement.

For preventing entrainment of air from occurring in molding process, ingeneral, it has been necessary to provide such measures that the lowerside of the hopper is cooled to decrease the temperature of the cylinderof the extruder, the rotation number of the screw is lowered, the backpressure is increased in the case of injection molding, and the like(see Non-patent Document 1), but even though these measures are made,there are cases where entrainment of air cannot be sufficientlyprevented from occurring due to the defective shape of the screw, andthere is a problem of deterioration in yield of products.

A polyamide resin composition excellent in extrusion property thatsuffers less unevenness in ejection and can lowers the extrusion forceupon melt extrusion molding has been disclosed (see Patent Document 1).Although the technique can improve the extrusion property upon extrusionmolding, there are cases where entrainment of air cannot be preventedfrom occurring depending on the shape of the screw. Furthermore, thereis no study relating to injection molding.

Since a m-xylylene group-containing polyamide has crystallinity, thereare cases where it is whitened due to crystallization immediately aftermolding to lower the transparency of the resulting product unlessmolding conditions such as an extrusion temperature, a coolingtemperature and a cooling time are properly set. For preventing thewhitening due to crystallization immediately after molding, a certaindegree of improvement can be obtained by decreasing the coolingtemperature or prolonging the cooling time, but the measures provide aproblem of deterioration in economy due to the prolonged cycle time.Furthermore, in such an apparatus that the cooling temperature cannot besufficiently lowered, or the cooling time cannot be prolonged, due tothe specification of the apparatus, the m-xylylene group-containingpolyamide cannot be used.

A polyamide molded article containing solid phase polymerizationpolyamide MXD6 that suffers less whitening upon storing under a highhumidity, upon making into contact with water or boiling water, or uponheating to a temperature of the glass transition temperature or higheris disclosed (see Patent Document 2), but there is no study relating toprevention of crystallization immediately after molding, and a polyamidethat is not formed by solid phase polymerization.

In a m-xylylene group-containing polyamide, carbon at the α-position ofthe benzene ring (benzyl carbon) is liable to be a radical, and thus itis poor in thermal stability as compared to a polyamide, such as nylon6. Accordingly, various proposals have been made relating to improvementin thermal stability upon production or extrusion molding process.

For example, for producing a m-xylylene group-containing polyamidehaving a less amount of gel, it is important to execute polycondensationin such a manner that the intended molecular weight is quickly obtainedwhile reducing the thermal history as much as possible. For reducing thethermal history, it is effective to execute the amidation reactionquickly by adding a compound having a catalytic effect into thepolycondensation system.

As the compound that catalyzes the amidation reaction, a phosphorusatom-containing compound has been widely known. Such a method has beenpreviously proposed that polycondensation for producing a polyamide iscarried out in the presence of a phosphorus atom-containing compound andan alkali metal compound (see, for example, Patent Document 3). Thephosphorus atom-containing compound not only accelerates the amidationreaction, but also functions as an antioxidant that prevents colorationof the polyamide due to oxygen present in the polycondensation system,and therefore a polyamide having a less amount of gel and having a lowyellowness degree can be obtained. However, the compound may bring aboutformation of a three-dimensional structure (gelation) in some cases, andthus a suitable addition amount is necessarily selected.

In the case where a polyamide having a phosphorus atom-containingcompound added in the polycondensation step is remelted and molded in anextruder or the like, however, there are cases where the resin pressureis gradually increased to fail to execute stable operation. As a resultof research on the reasons therefor by the inventors, it has been foundthat the phosphorus atom-containing compound contained in the polyamideat the filter mounted on the discharge port of the extruder is denaturedand deposited to clog the filter by attaching thereto.

Such a method has been proposed to prevent clogging of the filter bydecreasing the addition amount of the phosphorus atom-containingcompound, the alkali metal compound and the like added to the polyamide(see, for example, Patent Document 4). However, this method is differentfrom the present invention, which pays attention to denaturation of thephosphorus atom-containing compound. In this method, furthermore, sincethe addition amount of the phosphorus atom-containing compound forpreventing coloration of the polyamide is small, the resulting polyamideis colored yellow and has a low utility value as a packaging material.

A method for preventing gelation of a polyamide by adding from 0.0005 to0.5 part by weight of at least one kind selected from a lubricant, anorganic phosphorus stabilizer, a hindered phenol compound and a hinderedamine compound upon molding a polyamide has been proposed (see, forexample, Patent Document 5). However, this method relates to preventionof gelation of the polyamide due to the thermal history during moldingprocess, but there is no disclosure relating to clogging of the filterascribable to denaturation of the phosphorus atom-containing compound inthe polyamide.

A m-xylylene group-containing polyamide has various problems uponapplying as it is to a purpose that requires flexibility, such as a filmand the like, due to the considerably high rigidity thereof. Forimproving the property, various proposals for satisfying both the gasbarrier property and the flexibility have been made by melt-mixing anordinary polyamide excellent in flexibility, such as nylon 6, nylon 666and the like, with the m-xylylene group-containing polyamide, or byforming a multi-layer structure therewith (see, for example, PatentDocuments 6 to 8).

However, when the m-xylylene group-containing polyamide is mixed withanother nylon, there are cases where the melt viscosity is increased farbeyond the value that is expected from the arithmetic average. As ameasure for preventing the phenomenon, it has been proposed that thedifference in concentration between the end carboxyl group and the endamino group in the polyamide resin composition after melt-mixing has aparticular relationship to the concentration of the phosphorus atomcontained in the polyamide resin composition after melt-mixing (see, forexample, Patent Document 9). In this method, for suppressing theamidation from proceeding in the molten state, the balance of the endgroups of the polyamide is set to make one of them excessive, or theamount of the phosphorus compound capable of functioning as an amidationcatalyst is decreased, whereby the increase in melt viscosity due toincrease of the molecular weight is prevented from occurring. Uponproduction of a polyamide used for a packaging material and the like,however, a sufficient polymerization degree cannot be obtained unlessthe reaction molar ratio between the diamine component and thedicarboxylic acid is made close to 1 as much as possible. Accordingly,in this method, it is practically necessary to decrease theconcentration of the phosphorus atom in the polyamide to a low level. Inthe case where the concentration of the phosphorus atom in thepolymerization system is low, the polymerization reaction time forproviding a sufficient molecular weight is prolonged, and the resultingpolyamide has an increased yellowness degree and contains a large amountof gel due to oxidation of the polymer, whereby the products obtained bythe method, such as a packaging material and the like, are poor incommercial value consequently.

The inventors have found that the melt viscosity of the melt-mixedproduct of the m-xylylene group-containing polyamide and another nylonvaries in some cases depending on the production history, the storagecondition, the storage period and the like of the m-xylylenegroup-containing polyamide even though the melt viscosities, thephosphorus atom concentrations, the end group concentrations and thelike of the starting materials are the same. The problem, which is notdisclosed not only in Patent Document 9 but also in any document, isnecessarily resolved from the standpoint of extrusion process stability.

[Patent Document 1] JP-A-10-147711

[Patent Document 2] JP-A-2000-248176

[Patent Document 3] JP-A-49-45960

[Patent Document 4] JP-A-2005-194328

[Patent Document 5] JP-A-2001-164109

[Patent Document 6] JP-A-11-334006

[Patent Document 7] JP-A-2000-211665

[Patent Document 8] JP-A-2003-011307

[Patent Document 9] JP-A-7-247422

[Non-patent Document 1] “Shiritai Shashutsu Seikei” (Learning InjectionMolding), published by Japan Machinist Co., Ltd.

DISCLOSURE OF THE INVENTION

An object of the present invention is to solve the aforementionedproblems and to provide a polyamide resin composition that contains apolyamide containing a m-xylylene group and, depending on necessity,another polyamide, and has a less amount of gel, suffers lesscoloration, and can be stably subjected to molding process for aprolonged period of time. Another object of the present invention is toprovide a polyamide resin composition excellent in moldingprocessability and productivity that suffers less influence of moldingconditions, such as a screw shape and the like, and generates no bubblenot only on extrusion molding but also on injection molding. Stillanother object of the present invention is to provide a polyamide resincomposition that has good barrier property under a high humiditycondition, and suffers no whitening due to crystallization immediatelyafter molding, thereby providing a molded article excellent intransparency.

As a result of earnest investigations made by the inventors, theinventors have been found that a polyamide resin composition containinga m-xylylene group-containing polyamide obtained throughpolycondensation in the presence of a phosphorus atom-containingcompound mixed with a fatty acid metallic salt and, depending onnecessity, another additive causes no clogging of a filter to enablestable continuous operation for a prolonged period of time, provides amolded article with good appearance that suffers less gelation andcoloration, is excellent in molding processability and productivity, andprovides a molded article that is excellent in transparency and gasbarrier property under a high humidity condition. Furthermore, theinventors have found that a polyamide resin composition containing am-xylylene group-containing polyamide obtained through polycondensationin the presence of a phosphorus atom-containing compound mixed with afatty acid metallic salt and, depending on necessity, another additiveshows no abnormal increase of the melt viscosity to enable stablecontinuous operation for a prolonged period of time, and provides amolded article with good appearance that suffers less gelation andcoloration. The present invention is based on these findings.

Accordingly, the present invention relates to a polyamide resincomposition that contains a resin component containing a polyamide (X)obtained through melt polycondensation of a diamine component containing70% by mol or more of m-xylylenediamine and a dicarboxylic acidcomponent containing 70% by mol or more of an α,ω-linear aliphaticdicarboxylic acid, and a fatty acid metallic salt having from 10 to 50carbon atoms, and arbitrarily contains an additive (A) and/or anadditive (B), the additive (A) being at least one compound selected fromthe group consisting of a diamide compound obtained from a fatty acidhaving from 8 to 30 carbon atoms and a diamine having from 2 to 10carbon atoms, a diester compound obtained from a fatty acid having from8 to 30 carbon atoms and a diol having from 2 to 10 carbon atoms, and asurfactant, and the additive (B) being at least one compound selectedfrom the group consisting of a metallic hydroxide, a metallic acetatesalt, a metallic alkoxide, a metallic carbonate salt and a fatty acid.

BEST MODE FOR CARRYING OUT THE INVENTION

The polyamide resin composition of the present invention contains aresin component containing a polyamide (X), which is obtained throughpolycondensation of a diamine component containing 70% by mol or more ofm-xylylenediamine and a dicarboxylic acid component containing 70% bymol or more of an α,ω-linear aliphatic dicarboxylic acid, a fatty acidmetallic salt having from 10 to 50 carbon atoms, and depending onnecessity an additive (A) and/or an additive (B).

The diamine component constituting the polyamide (X) preferably containsm-xylylenediamine in an amount of 70% by mol or more, more preferably75% by mol or more, further preferably 80% by mol or more, andparticularly preferably 90% by mol or more (including 100% by mol). Inthe case where the amount of m-xylylenediamine in the diamine componentis 70% by mol or more, the resulting polyamide exhibits excellent gasbarrier property. Examples of a diamine other than m-xylylene diamineinclude an aliphatic diamine, such as tetramethylenediamine,pentamethylenediamine, 2-methyl-1,5-pentanediamine,hexamethylenediamine, heptamethylenediamine, octamethylenediamine,nonamethylenediamine, decamethylenediamine, dodecamethylenediamine,2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamineand the like; an alicyclic diamine, such as1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane,1,3-diaminocyclohexane, 1,4-diaminocyclohexane,bis(4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)propane,bis(aminomethyl)decalin, bis(aminomethyl)tricyclodecane and the like; adiamine having an aromatic ring, such as bis(4-aminophenyl)ether,p-phenylenediamine, p-xylylenediamine, bis(aminomethyl)naphthalene andthe like, but it is not limited thereto.

The dicarboxylic acid component constituting the polyamide (X)preferably contains an α,ω-linear aliphatic dicarboxylic acid in anamount of 70% by mol or more, more preferably 75% by mol or more,further preferably 80% by mol or more, and particularly preferably 90%by mol or more (including 100% by mol). In the case where the amount ofthe α,ω-linear aliphatic dicarboxylic acid is 70% by mol or more,decrease of the gas barrier property and excessive decrease of thecrystallinity can be prevented. The α,ω-linear aliphatic dicarboxylicacid is preferably at least one α,ω-linear aliphatic dicarboxylic acidhaving from 4 to 20 carbon atoms selected from succinic acid, glutaricacid, pimelic acid, adipic acid, sebacic acid, suberic acid, azelaicacid, undecanedioic acid, dodecanedioic acid, dimer acid and the like,and adipic acid is particularly preferred. Examples of the otherdicarboxylic acid component include an alicyclic dicarboxylic acid, suchas 1,4-cyclohexanedicarboxylic acid and the like, and an aromaticdicarboxylic acid, such as terephthalic acid, isophthalic acid,orthophthalic acid, xylylenedicarboxylic acid, naphthalenedicarboxylicacid and the like. In the case where the dicarboxylic acid componentcontains isophthalic acid in an amount of from 1 to 20% by mol, and morepreferably from 3 to 10% by mol, whitening immediately after molding canbe further suppressed.

In addition to the diamine component and the dicarboxylic acid componentmentioned above, as a component constituting the polyamide (X), alactam, such as ε-caprolactam, laurolactam and the like, an aliphaticaminocarboxylic acid, such as aminocaproic acid, aminoundecanoic acidand the like, an aromatic aminocarboxylic acid, such asp-aminomethylbenzoic acid and the like, and the lime may be used as acopolymerization component in such a range that does not impair theadvantages of the invention.

The polyamide (X) is preferably produced by a melt polycondensation(melt polymerization) method in the presence of a phosphorusatom-containing compound. Examples of the melt polycondensation methodinclude such a method that a nylon salt containing a diamine componentand a dicarboxylic acid component is heated under pressure in thepresence of water to polymerize in a molten state while removing theadded water and condensation water. It can also be produced by a methodof polycondensation by adding a diamine component directly into adicarboxylic acid component in a molten state. In this case, formaintaining the reaction system to a homogeneous liquid state, thediamine component is added continuously to the dicarboxylic acidcomponent, during which the polycondensation is carried out whileheating the reaction system to prevent the temperature thereof frombecoming lower than the melting points of the oligoamide and thepolyamide formed.

Examples of the phosphorus atom-containing compound includedimethylphosphinic acid, phenylmethylphosphinic acid, hypophosphorousacid, sodium hypophosphite, potassium hypophosphite, lithiumhypophosphite, ethyl hypophosphite, phenylphosphonous acid, sodiumphenylphosphonoate, potassium phenylphosphonoate, lithiumphenylphosphonoate, ethyl phenylphosphonoate, phenylphosphonic acid,ethyl phosphonic acid, sodium phenylphosphonate, potassiumphenylphosphonate, lithium phenylphosphonate, diethyl phenylphosphonate,sodium ethylphosphonate, potassium ethylphosphonate, phosphorous acid,sodium hydrogen phosphite, sodium phosphite, triethyl phosphite,triphenylphosphite, pyrrophosphorous acid and the like, and among these,a metallic hypophosphite salt, such as sodium hypophosphite, potassiumhypophosphite, lithium hypophosphite and the like, are preferably usedowing to the excellent coloration preventing effect thereof, with sodiumhypophosphite being particularly preferred. The phosphorusatom-containing compound capable of being used in the present inventionis not limited to these compounds.

The addition amount of the phosphorus atom-containing compound ispreferably from 50 to 400 ppm, more preferably from 60 to 350 ppm, andfurther preferably from 70 to 300 ppm, in terms of the phosphorus atomconcentration in the polyamide (X). In the case where the additionamount is in the range, the polyamide is prevented from being coloredduring polymerization, gelation reaction of the polyamide is suppressed,and a fish-eye, which is considered to be ascribable to the phosphorusatom-containing compound, can be prevented from being formed, therebyimproving the appearance of the resulting molded article.

The polycondensation for producing the polyamide (X) is preferablycarried out in the presence of an alkali metal compound (C) in additionto the phosphorus atom-containing compound. A sufficient amount of thephosphorus atom-containing compound is necessarily made present forpreventing coloration of the polyamide during polycondensation, whichmay bring about gelation of the polyamide in some cases, and therefore,an alkali metal compound (C) is preferably made present for controllingthe amidation reaction rate. As the alkali metal compound (C), an alkalimetal hydroxide and an alkali metal acetate salt are preferred. Examplesof the alkali metal compound (C) include lithium hydroxide, sodiumhydroxide, potassium hydroxide, rubidium hydroxide, cesium hydroxide,lithium acetate, sodium acetate, potassium acetate, rubidium acetate,cesium acetate and the like, but it is not limited to these compounds.

In the case where the polycondensation for producing the polyamide (X)is carried out in the presence of the alkali metal compound (C), theratio (molar number of the alkali metal compound (C))/(molar number ofthe phosphorus atom-containing compound) is preferably from 0.5 to 1,more preferably from 0.55 to 0.95, and further preferably from 0.6 to0.9. In the case where the ratio is in the range, the moderate effect ofsuppressing the acceleration of the amidation reaction by the phosphorusatom-containing compound can be obtained, and therefore, such aphenomenon can be avoided that the reaction is excessively suppressed tolower the polycondensation reaction rate, whereby the thermal history ofthe polyamide is increased to increase gelation of the polyamide.

The polyamide (X) obtained through polycondensation is once taken outand formed into pellets, which are used after drying. It may besubjected to solid phase polymerization for further increasing thepolymerization degree. As a heating apparatus for drying and solid phasepolymerization, a continuous heating and drying apparatus, a rotationdrum type heating apparatus, such as a tumbling dryer, a conical dryer,a rotary dryer and the like, and a cone-shaped heating apparatus havingrotary blades inside, which is referred to as Nauta mixer, arepreferably used, but it is not limited thereto, and known methods andapparatuses may be used. In the case where solid phase polymerization ofthe polyamide is carried out, in particular, a batchwise heatingapparatus is preferably used since the system can be sealed, wherebypolycondensation can be carried out in a state where oxygen causingcoloration is avoided.

The polyamide (X) obtained through the aforementioned process suffersless coloration and gelation, and in the present invention, among thepolyamides obtained through the aforementioned process, one having a b*value in the color difference test of JIS K7105 of 3 or less ispreferably used, particularly preferably 2 or less, and furtherpreferably 1 or less. The polyamide having a b* value exceeding 3 is notpreferred since it provides a molded article obtained through postprocessing having strong yellowness, which deteriorates the commercialvalue thereof.

A relative viscosity is ordinarily used as an index of thepolymerization degree of the polyamide (X). The relative viscosity ofthe polyamide (X) is preferably from 1.5 to 4.2, more preferably from1.7 to 4.0, and further preferably from 2.0 to 3.8. In the case wherethe polyamide (X) has a relative viscosity of 1.5 or more, the moltenpolyamide has stable flowability to provide a molded article excellentin appearance. In the case where the polyamide (X) has a relativeviscosity of 4.2 or less, the polyamide has a suitable relativeviscosity to execute the molding process stably. The relative viscosityreferred herein is a ratio of the drop time (t) of a solution of 1 g ofthe polyamide dissolved in 100 mL of 96% sulfuric acid measured with aCannon-Fenske viscometer at 25° C. to the drop time (t0) of 96% sulfuricacid itself measured in the same manner, and can be calculated from thefollowing expression.

Relative viscosity=t/t0

The number average molecular weight of the polyamide (X) is preferablyfrom 6,000 to 50,000, and more preferably from 10,000 to 45,000. In thecase where the number average molecular weight is in the range,favorable heat resistance and molding processability can be obtained.

The amount of melting heat of the polyamide (X) is preferably from 30 to70 J/g. In the case where the amount of melting heat is in the range,the polyamide resin composition can be easily melted in an extruder, andthe possibility of entraining air upon melting is lowered, and favorableproductivity and molding processability can be obtained.

The glass transition temperature (Tgm) of the polyamide (X) ispreferably from 70 to 100° C. In the case where the glass transitiontemperature is in the range, the polyamide resin composition can beeasily melted in an extruder, and the possibility of entraining air uponmelting is lowered, whereby favorable productivity and moldingprocessability can be obtained.

The degree of crystallinity of the polyamide (X) is preferably from 10to 40%. In the case where the degree of crystallinity is in the range,the polyamide resin composition can be easily melted in an extruder, andthe possibility of entraining air upon melting is lowered, wherebyfavorable productivity and molding processability can be obtained. Inthe case where the degree of crystallinity is too low, air is liable tobe entrained, and in the case where the degree of crystallinity is toohigh, a prolonged period of time is required for melting, and themoldability may be deteriorated in some cases. Furthermore, whiteningimmediately after molding can be suppressed.

The half crystallization time of the polyamide (X) at 160° C. ispreferably from 10 to 1,600 s, more preferably from 15 to 1,000 s, andfurther preferably from 20 to 500 s. In the case where the halfcrystallization time is in the range, the polyamide resin compositioncan be easily melted in an extruder, and the possibility of entrainingair upon melting is lowered, whereby favorable productivity and moldingprocessability can be obtained. Furthermore, whitening immediately aftermolding can be suppressed.

The melting point of the polyamide (X) is preferably from 200 to 265° C.In the case where the melting point is in the range, the polyamide resincomposition can be easily melted in an extruder, and the possibility ofentraining air upon melting is lowered, whereby favorable productivityand molding processability can be obtained.

The melting point, the amount of melting heat and the glass transitiontemperature were measured by the DSC (differential scanning calorimetermeasurement) method. DSC-50, produced by Shimadzu Corporation, was used,and about 5 mg of a sample was heated from room temperature to 300° C.at a temperature increasing rate of 10° C. per minute. As theatmospheric gas, nitrogen was fed at 30 mL/min. As the glass transitiontemperature, the so-called median point temperature (Tgm) was used. Tgmis the median point temperature of two intersecting points of thetangent lines of the base lines of the glass state and the supercooledstate (rubber state) and the tangent line of the slope showing thetransition state. The degree of crystallinity was calculated by usingthe amount of crystallization heat and the amount of melting heatobtained by the DSC method. The half crystallization time was obtainedby the depolarization intensity method. The polyamide (X) wasmelt-extruded from an extruder through a T-die at from 240 to 270° C.The resulting sheet having a thickness of about from 100 to 200 μm washeld with two glass plates and melted in an air bath at 280° C. for 3minutes, and then the sheet was placed in an oil bath at 160° C. andmeasured for depolarization transmitted light intensity. As an apparatustherefor, for example, one produced by Kotaki Manufacturing Co., Ltd.(polymer crystallization rate measuring apparatus, MK-701) and the likecan be used.

The polyamide (X) may contain additives, such as a matting agent, a heatresistant stabilizer, a weather resistant stabilizer, an ultraviolet rayabsorbent, a nucleating agent, a plasticizer, a flame retardant, anantistatic agent, a coloration preventing agent, a gelation preventingagent and the like, various organic compounds for sealing the ends,clay, such as bedded silicate and the like, a nanofiller and the like,but it is not limited to those described above, and various materialsmay be added during polymerization and after polymerization.

A molded article obtained by molding the polyamide (X) as it isexcellent in appearance without coloration and gelation, but there maybe some cases where a filter, which is generally provided in the moldingapparatus for removing foreign matters, is clogged to increase the resinpressure, whereby the quality of the product may be fluctuated, andoperation of the apparatus is necessarily stopped within a short periodof time to deteriorate the production efficiency. This is because thephosphorus atom-containing compound remaining in the polyamide (X) isdenatured and deposited through the thermal history to clog the filter.

The resin component of the polyamide resin composition of the presentinvention may be the polyamide (X) solely or may contain a polyamide (Y)in addition to the polyamide (X).

As the polyamide (Y), a polyamide that does not contain am-xylylenediamine unit is used. Examples thereof include an aliphaticpolyamide, such as nylon 6, nylon 66, nylon 666, nylon 46, nylon 610,nylon 612 and the like, a semi-aromatic polyamide, such as nylon 6T,nylon 6I, nylon 6IT, nylon 9T, nylon 66I and the like, and a copolymerthereof, which may be selected depending on purpose. As the polyamide(Y), one of those described above may be used, and two or more of themmay be used after mixing depending on purpose. For example, in the casewhere flexibility is demanded, nylon 6 and nylon 666 are preferablymixed. For increasing the crystallization rate of the polyamide (X), acrystalline polyamide, such as nylon 6, nylon 66 and the like, ispreferably mixed, and for decreasing the same, anon-crystalline orhardly crystalline polyamide, such as nylon 6IT and the like, ispreferably mixed.

The polyamide (Y) is produced by the melt polycondensation (meltpolymerization) method. In the polycondensation of the polyamide (Y),the phosphorus atom-containing compound may be added for increasing theamidation reaction rate. Furthermore, for increasing the polymerizationdegree, it may be subjected to solid phase polymerization as similar tothe polyamide (X).

The polymerization degree of the polyamide (Y) is preferably selectedwith the melt viscosity at the temperature, at which it is melted andmixed with the polyamide (X), as an index. Upon mixing the polyamide (X)and the polyamide (Y), the morphology thereof forms a sea-islandstructure, in which there is a tendency that a smaller dispersedparticle diameter of the island part provides a composition havingexcellent characteristics. Specifically, upon mixing the polyamide (X)and the polyamide (Y), it is preferred that the melt viscosity of thelarge amount component is larger than the melt viscosity of the smallamount component, and it is more preferred that the melt viscosity ofthe large amount component is 1.2 times or more, and further preferably1.5 times or more, the melt viscosity of the small amount component.

The melt viscosity of the polyamide resin composition at 270° C. and ashear rate of 100 s⁻¹ is preferably 1.20 times or less, more preferablyfrom 1 to 1.20 times, and further preferably from 1 to 1.15 times, thearithmetic average value obtained by the following expression (1):

MVA=MV1/(W1/100)+MV2/(W2/100)  (1)

(In the expression, MVA represents the arithmetic average value of themelt viscosity (Pa·s);

MV1 represents the melt viscosity (Pa·s) of the polyamide (X) at 270° C.and a shear rate of 100 s⁻¹;

MV2 represents the melt viscosity (Pa·s) of the polyamide (Y) at 270° C.and a shear rate of 100 s⁻¹;

W1 represents the weight ratio (% by weight) of the polyamide (X) in thepolyamide resin composition; and

W2 represents the weight ratio (% by weight) of the polyamide (Y) in thepolyamide resin composition.)

The polyamide (Y) may contain additives, such as a matting agent, a heatresistant stabilizer, a weather resistant stabilizer, an ultraviolet rayabsorbent, a nucleating agent, a plasticizer, a flame retardant, anantistatic agent, a coloration preventing agent, a gelation preventingagent and the like, various organic compounds for sealing the ends,clay, such as bedded silicate and the like, a nanofiller and the like,but it is not limited to those described above, and various materialsmay be added during polymerization and after polymerization.

The mixing ratio of the polyamide (X) and the polyamide (Y) ispreferably (polyamide (X))/(polyamide (Y)) of (from 1 to 99)/(from 99to 1) (% by weight with 100% by weight in total), more preferably (from5 to 95)/(from 95 to 5), and further preferably (from 10 to 90)/(from 90to 10). In the case where the ratio is in the range, the modificationeffect by mixing the polyamide (X) and the polyamide (Y) can besufficiently obtained.

In the present invention, for improving molding processability andpreventing denaturation of the phosphorus atom-containing compoundoccurring in the molding process to prevent the melt viscosity frombeing largely increased, a fatty acid metallic salt and, depending onnecessity an additive (A) and/or an additive (B) are added to thepolyamide (X) or a mixture of the polyamide (X) and the polyamide (Y).In the case where the fatty acid metallic salt and the additive (A)arbitrarily added are present in the melted polyamide (X) or mixture ofthe polyamide (X) and the polyamide (Y), the molding processability isparticularly improved. In the case where the fatty acid metallic saltand the arbitrary additive (B) are present in the melted polyamide (X),denaturation of the phosphorus atom-containing compound, which causesclogging of the filter, can be particularly suppressed. In the casewhere the fatty acid metallic salt and the arbitrary additive (B) arepresent in the melted mixture of the polyamide (X) and the polyamide(Y), the melt viscosity can be particularly prevented from being largelyincreased.

The carbon number of the fatty acid constituting the fatty acid metallicsalt is from 10 to 50, and more preferably 18 to 34. The fatty acid maycontain a side chain and a double bond, and is preferably a linearsaturated fatty acid, such as stearic acid (C18), eicosanoic acid (C20),behenic acid (C22), montanic acid (C28), triacontanoic acid (C30) andthe like. Examples of the metal constituting the salt with the fattyacid include sodium, potassium, lithium, calcium, barium, magnesium,strontium, aluminum, zinc, cobalt and the like, and sodium, potassium,lithium, calcium, aluminum and zinc are preferred. The fatty acidmetallic salt may be one of those described above or may be used incombination of two or more of them. The fatty acid metallic salt isexcellent in handleability as compared to hydroxides and acetate salts,and among these, a stearate metallic salt, particularly calciumstearate, is preferred since it is inexpensive and has a function oflubricant capable of further stabilizing the molding process.

The addition amount of the fatty acid metallic salt is preferably from50 to 5,000 ppm, more preferably from 100 to 3,000 ppm, and furtherpreferably from 100 to 1,000 ppm, in the polyamide resin composition. Inthe case where the addition amount is in the range, high effects ofprevention of air entrainment and prevention of whitening can beobtained to improve productivity and molding processability.

The additive (A) is at least one compound selected from the groupconsisting of a diamide compound, a diester compound and a surfactant.

The diamide compound is obtained from a fatty acid having from 8 to 30carbon atoms and a diamine having from 2 to 10 carbon atoms. In the casewhere the carbon number of the fatty acid is 8 or more, and the carbonnumber of the diamine is 2 or more, whitening prevention effect can beexpected. In the case where the carbon number of the fatty acid is 30 orless, and the carbon number of the diamine is 10 or less, the polyamideresin composition attains favorable homogeneous dispersion. The fattyacid may have a side chain or a double bond, and is preferably a linearsaturated fatty acid, such as stearic acid (C18), eicosanoic acid (C20),behenic acid (C22), montanic acid (C28), triacontanoic acid (C30) andthe like. Examples of the diamine include ethylenediamine,butylenediamine, hexanediamine, xylylenediamine,bis(aminomethyl)cyclohexane and the like. A diamide compound obtainedfrom a fatty acid having from 8 to 30 carbon atoms and a diamine mainlycontaining ethylene diamine, and a diamide compound obtained from afatty acid mainly containing montanic acid and a diamine having from 2to 10 carbon atoms are preferred. Among these, ethylenebisstearylamideis particularly preferred.

The diester compound is obtained from a fatty acid having from 8 to 30carbon atoms and a diol having from 2 to 10 carbon atoms. In the casewhere the carbon number of the fatty acid is 8 or more, and the carbonnumber of the diol is 2 or more, whitening prevention effect can beexpected. In the case where the carbon number of the fatty acid is 30 orless, and the carbon number of the diol is 10 or less, the polyamideresin composition attains favorable homogeneous dispersion. The fattyacid may have a side chain or a double bond, and is preferably a linearsaturated fatty acid, such as stearic acid (C18), eicosanoic acid (C20),behenic acid (C22), montanic acid (C28), triacontanoic acid (C30) andthe like. Examples of the diol include ethylene glycol, propanediol,butanediol, hexanediol, xylylene glycol, cyclohexanedimethanol and thelike. A diester compound obtained from a fatty acid mainly containingmontanic acid and a diol mainly containing ethylene glycol and1,3-butanediol is particularly preferred.

The surfactant is selected from a nonionic surfactant, an anionicsurfactant and a cationic surfactant. Examples of the nonionicsurfactant include a polyethylene glycol surfactant of an ester type, anether type and an alkylphenol type, a polyhydric alcohol partial estersurfactant of a sorbitan ester type, an ester ether surfactant of apolyoxyethylenesorbintan ester type, and the like, and it is not limitedthereto. In the present invention, polyoxyethylenesorbitan monolaurate,which is one kind of an ester ether surfactant of apolyoxyethylenesorbintan ester type, is preferably used since it hasparticularly excellent air entrainment prevention effect and whiteningprevention effect. The kinematic eddy viscosity of the nonionicsurfactant is preferably about from 200 to 1,000 mm²/s, and morepreferably about from 250 to 500 mm²/s, at 25° C. In the case where thekinematic eddy viscosity is in the range, favorable dispersibility andhigh air entrainment prevention effect are obtained to improveproductivity and molding processability.

The additive (A) may be used solely or in combination of two or morekinds thereof. In the case where the diamide compound and/or the diestercompound are used as the additive (A), the addition amount thereof ispreferably from 50 to 1,000 ppm, more preferably from 100 to 800 ppm,and particularly preferably from 200 to 500 ppm, in the polyamide resincomposition. In the case where the addition amount is in the range, highair entrainment prevention effect and whitening prevention effect areobtained to improve productivity and molding processability. In the casewhere the surfactant is used as the additive (A), the addition amountthereof is preferably from 50 to 500 ppm, and more preferably from 70 to250 ppm, in the polyamide resin composition. In the case where theaddition amount is in the range, high air entrainment prevention effectand whitening prevention effect are obtained to improve productivity andmolding processability. In the case where the fatty acid metallic saltand the surfactant are used in combination, the addition amounts thereofare preferably from 100 to 1,000 ppm for the fatty acid metallic saltand from 50 to 200 ppm for the surfactant, and more preferably from 200to 500 ppm for the fatty acid metallic salt and from 70 to 150 ppm forthe surfactant, in the polyamide resin composition. As the additive (A),the nonionic surfactant is preferred, combination use of the fatty acidmetallic salt is more preferred, and combination use of calcium stearateand polyoxyethylenesorbitan monolaurate is further preferred.

Examples of the additive (B) include a metallic hydroxide, such aslithium hydroxide, sodium hydroxide, potassium hydroxide, rubidiumhydroxide, cesium hydroxide and the like; a metallic acetate salt, suchas lithium acetate, sodium acetate, potassium acetate, rubidium acetate,cesium acetate and the like; a metallic alkoxide, such as sodiummethoxide, sodium ethoxide, sodium propoxide, sodium butoxide, potassiummethoxide, lithium methoxide and the like; a metallic carbonate salt,such as sodium carbonate and the like; a fatty acid; and the like, butit is not limited thereto.

The additive (B) encompasses the same compounds as the alkali metalcompound (C) capable of being added during the polycondensation reactionfor producing the polyamide (X), but it is considered that the alkalimetal compound (C) is ionized in the polycondensation system, and theanions (such as OH⁻ and CH₃COO⁻) formed from the alkali metal compound(C) in the dehydration step for executing the polycondensation reactionbecome water or acetic acid or are discharged along with water, wherebythe alkali metal compound (C) is not present in the original form.Accordingly, it is expected that the alkali metal compound (C), which isadded upon producing the polyamide (X), cannot attain the function ofpreventing the phosphorus atom-containing compound from being denaturedupon molding. In the present invention, an alkali metal compound that isadded during the polycondensation reaction is referred to as the alkalimetal compound (C), which is distinguished from an alkali metal compoundthat is added as the additive (B).

The addition amounts of the fatty acid metallic salt and the arbitraryadditive (B) are preferably such amounts that provide a ratiorepresented by the expression:

M1/M2

(in the expression, M1 represents the total molar number of the fattyacid metallic salt and the additive (B) in the polyamide resincomposition, and M2 represents the molar number of the phosphorusatom-containing compound used in the polycondensation for producing thepolyamide (X) in the polyamide resin composition) in a range of from0.05 to 0.5, more preferably from 0.07 to 0.4, and further preferablyfrom 0.1 to 0.3. In the case where the ratio is 0.05 or more, thephosphorus atom-containing compound can be prevented from beingdenatured to prevent clogging of the filter. In the case where the ratiois 0.5 or less, the polyamide (X) can be prevented from being decomposedand colored during molding. The addition amount of the fatty acidmetallic salt has been described above. In the case where the additionamount is in the range, the polyamide resin composition can be stablyprocessed.

In the case where the resin component contains the polyamide (X) and thepolyamide (Y), the addition amounts of the fatty acid metallic salt andthe additive (B) are preferably such amounts that provide a ratiorepresented by the expression:

M3/M4

(in the expression, M3 represents the total molar number of the fattyacid metallic salt and the additive (B) in the polyamide resincomposition, and M4 represents the total molar number of the phosphorusatom-containing compound used in the polycondensation for producing thepolyamide (X) and the phosphorus atom-containing compound used in thepolycondensation for producing the polyamide (Y) in the polyamide resincomposition) in a range of from 0.05 to 0.5, more preferably from 0.07to 0.4, and further preferably from 0.1 to 0.3. In the case where theratio is 0.05 or more, increase of the melt viscosity due to thephosphorus atom-containing compound can be suppressed, and in the casewhere the ratio is 0.5 or less, the polyamide (X) and the polyamide (Y)can be prevented from being hydrolyzed with the fatty acid salt and theadditive (B) or being colored upon molding. The addition amount of thefatty acid metallic salt has been described above.

As having been described above, there are cases where a high meltviscosity far exceeding the arithmetic average is exhibited uponmelt-mixing the polyamide (X) and the polyamide (Y). While the reasonwhy the melt viscosity is greatly increased is not clear, such aphenomenon is not observed in the case where the amount of thephosphorus atom-containing compound in the polyamide resin compositionis considerably small, and it is thus expected that amide exchangereaction proceeds between the polyamide (X) and the polyamide (Y)through the amidation catalytic effect of the phosphorus atom-containingcompound, whereby a polyamide having a high molecular weight isproduced. The fatty acid salt and the additive (B) also have a functionof preventing the increase of the melt viscosity.

The phosphorus atom-containing compound has a function of preventing thepolyamide (X) from being oxidized as having been described above, andfor example, when the polyamide (X) having been stored for a certainperiod or the polyamide (X) having been exposed to the air is used asthe resin component, the degree of increase of the melt viscositysometimes varies even though the phosphorus atom concentration and theend group concentration are the same. It is considered that this isbecause the phosphorus atom-containing compound is reacted with oxygento lose the catalytic effect to amidation reaction, and the effect ofaccelerating the amide exchange reaction upon mixing with the polyamide(Y) is gradually lost. However, by adding the fatty acid metallic saltand the arbitrary additive (B) in suitable amounts, a melt viscositythat is close to the arithmetic average calculated from the meltviscosities of the polyamide (X) and the polyamide (Y) can be realizedirrespective of the storage state of the polyamide (X). The addition ofthe fatty acid metallic salt and the arbitrary additive (B) decreasesthe effect of the amount of the phosphorus atom-containing compoundcontained in the polyamide (X) and the polyamide (Y) and the end groupconcentration of the polyamides on the melt viscosity, and thus thepolyamide resin composition can be produced by selecting the polyamide(X) and the polyamide (Y) having properties corresponding to the purposewithout care of the end group concentration of the polyamides and thephosphorus atom concentration.

In the present invention, the additive (A) and the additive (B) are notparticularly limited in shape, and preferably have a particle diameterof 0.2 mm or less since powder having a small particle diameter can beeasily dispersed uniformly in the resin composition through dry mixing.

The resin component (the polyamide (X), or the polyamide (X) and thepolyamide (Y)) can be mixed with the fatty acid metallic salt and thearbitrary additive (A) and/or the arbitrary additive (B) by a knownmethod, and dry mixing is preferably performed since it is low in costand does not apply thermal history. In the case where the resincomponent is a mixture of the polyamide (X) and the polyamide (Y), it ispreferably added upon melt mixing. Examples of the dry mixing methodinclude a method of placing the resin component, the fatty acid metallicsalt and the arbitrary additive (A) and/or the arbitrary additive (B) ina tumbler, which is rotated for mixing them. Examples thereof alsoinclude a method of producing a master batch containing the polyamide(X), the polyamide (Y) and other thermoplastic resins kneaded with thefatty acid metallic salt and the arbitrary additive (A) and/or thearbitrary additive (B). The substrate of the master batch is preferablya thermoplastic resin that does not change the properties of thepolyamide resin composition largely. The polyamide (X) or the polyamide(Y) is particularly preferably used as the substrate. However, in thecase where the mixing amount of the master batch is not significantlylarge, the substrate may be selected from various thermoplastic resinswithout particular limitation. Furthermore, such a method may beemployed that for preventing separation of the fatty acid metallic salt,the additive (A) and the additive (B) from the resin component, aviscous liquid is attached as a spreading agent to the resin component,and then the components are added and mixed. Examples of the spreadingagent include a surfactant but are not limited thereto, and knownproducts may be used.

The polyamide resin composition may contain one or plural kinds of otherresins, such as a polyester resin, a polyolefin resin, a phenoxy resinand the like, in such a range that does not impair the objects of theinvention. Furthermore, a fibrous inorganic filler, such as glassfibers, carbon fibers and the like; a tabular inorganic filler, such asglass flakes, talc, kaolin, mica, montmorillonite, organized clay andthe like; an impact resistance improving agent, such as various kinds ofelastomer and the like; a crystal nucleating agent; a lubricant, such asa fatty acid amide compound, a fatty acid metallic salt compound, afatty acid amide compound and the like; an antioxidant, such as a coppercompound, an organic or inorganic halogen compound, a hindered phenolcompound, a hindered amine compound, a hydrazine compound, a sulfurcompound, a phosphorus compound and the like; an additive, such as aheat stabilizer, a coloration preventing agent, an ultraviolet rayabsorbent, e.g., a benzotriazole compound and the like, a releasingagent, a plasticizer, a colorant, a flame retardant and the like; and anadditive, such as a compound containing metallic cobalt, which is acompound imparting oxygen scavenging capability, an alkali compound forpreventing the polyamide from being gelled, and the like may be added.

The polyamide resin composition of the present invention can be appliedto not only various packaging materials, such as a film, a sheet, abottle and the like, but also various materials including amonofilament, a molding material and the like. Upon forming a packagingmaterial, other thermoplastic resins, a metallic foil, a paperboard andthe like may be used in combination. The polyamide resin composition ofthe present invention may be melt-mixed with other thermoplastic resinsdepending on necessity.

The polyamide resin composition of the present invention preferably hasan oxygen transmission rate (OTR) of 0.2 cc·mm/(m²·day·atm) or less,more preferably 0.15 cc·mm/(m²·day·atm) or less, further preferably 0.10cc·mm/(m²·day·atm) or less, and particularly preferably 0.08cc·mm/(m²·day·atm) or less, in terms of an average value underconditions of a temperature of 23° C. and a relative humidity (RH) of60%. A bottle having a barrier layer exhibiting such an OTR capabilityhas a favorable gas barrier property, which prolongs the expirationperiod of the content stored.

Accordingly, a barrier layer of a multilayer structure is preferablyformed with the polyamide resin composition of the present inventionsince it is good in gas barrier property, productivity, moldingprocessability and transparency. Examples of the multilayer structureinclude a multilayer film, a multilayer sheet, a multilayer bottle, amultilayer blown bottle and the like.

The multilayer structure is not particularly limited in productionmethod, and known techniques may be used. For example, a film is formedby a co-extrusion method and then formed into various containers.Examples of the co-extrusion method include known methods, such as aT-die method, an inflation method and the like. A multilayer preform maybe produced by injection molding, and then formed into a multilayerbottle by blow molding. In the case where the polyamide resincomposition of the present invention is used as a barrier layer, inparticular, high bubble entrainment prevention effect and whiteningprevention effect are obtained upon producing the multilayer preform,thereby improving favorably the productivity and transparency.

In the production of the multilayer structure using the polyamide resincomposition of the present invention as a barrier layer, a known screw,such as those for nylon or polyolefin, those of a slow compression typeand a rapid compression type, those of a single flight type and a doubleflight type, and the like, may be used, and molding can be favorablyperformed without bubbles entrained with such a screw that has been saidto be unsuitable for extruding MXD6.

The cylinder temperature, at which the polyamide resin composition ofthe present invention is extrusion-molded or injection-molded into abarrier layer, is preferably from 200 to 300° C., and more preferablyfrom 210 to 290° C. The rotation number of the screw is preferably from5 to 400 rpm, and more preferably from 10 to 250 rpm. The backpressureupon measuring for injection molding is preferably from 0 to 1,000 psi,and more preferably from 25 to 500 psi.

The multilayer structure of the present invention can be applied to abag container, such as a bag sealed on four edges, a pillow bag, astanding pouch bag and the like, various packaging materials, such as alid material for a container and the like, a bottle, and the like. Astretched film may be produced with the multilayer film as a rawmaterial and formed into a container. The multilayer non-stretched filmmay be heat-molded into a container in a cup form. A multilayerstructure may be produced by laminating with paper. The multilayerstructure of the present invention can house and store various products.For example, it can house various products, such as a liquid beverage, aseasoning, a food in a paste form, a food in a liquid form, noodles, aprocessed rice product, a dairy product, a chemical agent in a solidform or a liquid form, a medical agent in a liquid form or a paste form,a cosmetic material, a hair-care product, a skin-care product, anelectronic part and the like.

In particular, the multilayer structure of the present invention issuitable for a material of a packaging container housing a producthaving a high water activity, a packaging container exposed to a highhumidity, and a packaging container subjected to thermal sterilization,such as retorting, boiling and the like.

The multilayer structure of the present invention has a layer (layer(2)) other than the barrier layer (layer (1)). The material forconstituting the layer (2) is not particularly limited, and examplesthereof include polyester, polyolefin, polyamide, polystyrene, paper andthe like.

The layer (2) is preferably a layer constituted mainly with polyester.The polyester is preferably a thermoplastic polyester resin obtainedthrough polymerization reaction of a dicarboxylic acid componentcontaining terephthalic acid in an amount of 80% by mol or more, andpreferably 90% by mol or more, and a diol component containing ethyleneglycol in an amount of 80% by mol or more, and preferably 90% by mol ormore (which is hereinafter referred to as a polyester (F)).

As the polyester (F), polyethylene terephthalate is preferably used.Polyethylene terephthalate is preferred since it exhibits excellentcharacteristics in transparency, mechanical strength, injection moldingproperty, stretching blow-molding property and the like.

As the other dicarboxylic acid component than terephthalic acid in thepolyester (F) isophthalic acid, diphenylether-4,4′-dicarboxylic acid,naphthalene-1,4 or 2,6-dicarboxylic acid, adipic acid, sebacic acid,decane-1,10-dicarboxylic acid and hexahydroterephthalic acid may beused. As the other diol component than ethylene glycol, propyleneglycol, 1,4-butanediol, neopentyl glycol, diethylene glycol,cyclohexanedimethanol, 2,2-bis(4-hydroxyphenyl)propane,2,2-bis(4-hydroxyethoxyphenyl)propane and the like may be used.Furthermore, an oxy acid, such as p-oxybenzoic acid and the like, may beused as a raw material monomer of the polyester (F).

The intrinsic viscosity of the polyester (F) is from 0.55 to 1.30,preferably from 0.65 to 1.20, and particularly preferably from 0.7 to1.0 (solvent: mixed solvent phenol/tetrachloroethane=6/4, measurementtemperature: 30° C.). In the case where the intrinsic viscosity is 0.55or more, a multilayer preform can be obtained in a transparent amorphousstate, and a multilayer bottle obtained has a satisfactory mechanicalstrength. In the case where the intrinsic viscosity is 1.30 or less, abottle can be easily molded with flowability not lost upon molding.

The polyester (F) may contain other thermoplastic resins and variousadditives in such ranges that do not impair the advantages of theinvention. Examples of the thermoplastic resin include a thermoplasticpolyester resin, such as polyethylene 2,6-naphthalenedicarboxylate andthe like, a polyolefin resin, polycarbonate, polyacrylonitrile,polyvinyl chloride, polystyrene and the like. Examples of the additiveinclude an ultraviolet ray absorbent, an oxygen absorbent, a colorant,an infrared ray absorbent that accelerates heating of the preform toshorten the cycle time on molding (reheat additive) and the like.

A polyamide compound is preferably used in the layer (2), and analiphatic polyamide is particularly preferably used since it providesgood mechanical properties without impairing the appearance of the film.As the aliphatic polyamide resin, copolymers, such as nylon 6, nylon 66,nylon 46, nylon 610, nylon 612, nylon 11, nylon 12, nylon 666 and thelike, may be used solely or in combination of plural kinds thereof.Among these, nylon 6, nylon 66 and nylon 666 are preferably used sincethey exhibit high effect of improving the mechanical properties of thefilm. The layer (2) is preferably a layer that is constituted mainly byan aliphatic polyamide.

In the layer (2), for example, various kinds of polyolefin materials arepreferably used since the mechanical properties of the multilayerstructure can be improved, such as a polyethylene material, such as lowdensity polyethylene, medium density polyethylene, high densitypolyethylene and the like, a polypropylene material, such as a propylenehomopolymer, a propylene-ethylene block copolymer, a propylene-ethylenerandom copolymer and the like, an ethylene-butene copolymer, anethylene-hexene copolymer, an ethylene-octene copolymer, anethylene-vinyl acetate copolymer, an ethylene-methyl methacrylatecopolymer, a propylene-α-olefin copolymer, polybutene, polypentene, anionomer resin and the like. The layer (2) is preferably a layer that isconstituted mainly by a polyolefin material.

The layer (2) may contain, for further improving the mechanicalproperties, an impact resistance improving material, such as variouskinds of elastomer and the like, and may contain additives, for example,a crystal nucleating agent, a lubricant, such as a fatty acid amidecompound, a fatty acid metallic salt compound, a fatty acid amidecompound and the like, an antioxidant, such as a copper compound, anorganic or inorganic halogen compound, a hindered phenol compound, ahindered amine compound, a hydrazine compound, a sulfur compound, aphosphorus compound, e.g., sodium hypophosphite, potassiumhypophosphite, calcium hypophosphite, magnesium hypophosphite and thelike, a heat stabilizer, a coloration preventing agent, an ultravioletray absorbent, e.g., a benzotriazole compound and the like, a releasingagent, a plasticizer, a colorant, a flame retardant and the like, andmay contain an inorganic pigment, such as titanium oxide and the like,and an organic pigment, such as a dye and the like.

The multilayer structure of the present invention may have an adhesiveresin layer containing a modified polyolefin resin or the like laminatedbetween the layers depending on necessity.

The multilayer structure of the present invention may have such a layerlaminated thereon that functions as a sealant upon used as a packagingmaterial, such as a pouch, a lid and the like. A thermoplastic resincapable of being used as the sealant is not particularly limited as faras it exhibits the function of sealant, and examples thereof includevarious kinds of polyolefin, for example, a polyethylene material, suchas low density polyethylene, medium density polyethylene, high densitypolyethylene and the like, a polypropylene material, such as a propylenehomopolymer, a propylene-ethylene block copolymer, a propylene-ethylenerandom copolymer and the like, an ethylene-butene copolymer, anethylene-hexene copolymer, an ethylene-octene copolymer, anethylene-vinyl acetate copolymer, an ethylene-methyl methacrylatecopolymer, a propylene-α-olefin copolymer, polybutene, polypentene, anionomer resin and the like, polystyrene, a polyester resin, such aspolyethylene terephthalate and the like, a thermoplastic resin havingeasy-peeling property, and the like. The sealant layer may be a singlelayer containing the aforementioned resins or may have a multilayerstructure having two or more layers. In the case of the multilayerstructure, an adhesive resin layer containing a modified polyolefinresin or the like may be laminated between the resin layers depending onnecessity.

The sealant layer may contain an impact resistance improving material,such as various kinds of elastomer and the like, and may containadditives, for example, a crystal nucleating agent, a lubricant, such asa fatty acid amide compound, a fatty acid metallic salt compound, afatty acid amide compound and the like, an antioxidant, such as a coppercompound, an organic or inorganic halogen compound, a hindered phenolcompound, a hindered amine compound, a hydrazine compound, a sulfurcompound, a phosphorus compound, e.g., sodium hypophosphite, potassiumhypophosphite, calcium hypophosphite, magnesium hypophosphite and thelike, a heat stabilizer, a coloration preventing agent, an ultravioletray absorbent, e.g., a benzotriazole compound and the like, a releasingagent, a plasticizer, a colorant, a flame retardant and the like, andmay contain an inorganic pigment, such as titanium oxide and the like,and an organic pigment, such as a dye and the like, in such a range thatdoes not impair the function as sealant.

For improving the mechanical property or enhancing the commercial value,the multilayer structure of the present invention may have anon-stretched or stretched film containing polyester, polyamide,polypropylene or the like laminated thereon by extrusion lamination, drylamination or the like.

In the case where the polyamide resin composition of the presentinvention is used as a barrier layer of a multilayer bottle, growth ofspherulite in the barrier layer can be suppressed to improve favorablythe delamination resistance of the multilayer bottle. The multilayerbottle can be obtained by subjecting a multilayer preform, which isobtained, for example, with an injection molding machine having twoinjection cylinders by injecting the layer (2) forming material and thepolyamide resin composition from the injection cylinders on the skinside and the core side respectively through a die hot runner into a diecavity, to biaxially stretching blow molding according to a knownmethod.

In general, a multilayer preform is blow-molded by a known methodincluding so-called a cold parison method, a hot parison method and thelike. Examples of the method include a method, in which after heating asurface of a multilayer preform to 80 to 120° C., the preform isstretched in the axial direction with a mechanical measure, such as corerod insertion and the like, and then stretched in the transversaldirection by blowing high-pressure air of generally from 2 to 4 MPa toattain blow molding, a method, in which a neck part of a multilayerpreform is crystallized, and after heating the surface of the preform to80 to 120° C., the preform is blow-molded in a mold at 90 to 150° C.,and the like.

In the present invention, the heating temperature of the preform ispreferably from 90 to 110° C., and more preferably from 95 to 108° C. Inthe case where the temperature is in the range, the multilayer preformcan be favorably molded into a bottle. The surface temperature can bemeasured with an infrared radiation thermometer at a general emissivityof 0.95.

The weight of the multilayer preform is preferably from 15 to 50 g. Itis preferably from 18 to 30 g for the preform for a bottle of about 500mL, and is preferably from 15 to 25 g for the preform for a bottle ofabout 350 mL. In the case where the weight is in the range, themultilayer preform can be favorably molded into a bottle with good gasbarrier property.

In the present invention, the multilayer bottle preferably has athree-layer structure including layer (2)/layer (1)/layer (2) or afive-layer structure including layer (2)/layer (1)/layer (2)/layer(1)/layer (2) owing to excellent barrier property and moldability.

A multilayer bottle having a three-layer structure or a five-layerstructure can be obtained by subjecting a multilayer preform having athree-layer structure or a five-layer structure to biaxially stretchingblow molding according to a known method. The cooling time for formingthe multilayer preform is preferably 2 seconds or more, and morepreferably 3 seconds or more. The temperature of cooling water ispreferably 15° C. or less. The multilayer preform having a three-layerstructure or a five-layer structure is not particularly limited inproduction method thereof, and a known method may be applied. Forexample, the layer (2) forming material constituting the innermost layerand the outermost layer is injected from the injection cylinder on theskin side, and the polyamide resin composition constituting the barrierlayer (layer (1)) is injected from the injection cylinder on the coreside, in which the layer (2) forming material is firstly injected, thenthe polyamide resin composition and the layer (2) forming material aresimultaneously injected, and then the layer (2) forming material isinjected in a necessary amount to fill the mold cavity, whereby themultilayer preform having a three-layer structure (layer (2)/layer(1)/layer (2)) can be produced.

The layer (2) forming material constituting the innermost layer and theoutermost layer is injected from the injection cylinder on the skinside, and the polyamide resin composition constituting the barrier layeris injected from the injection cylinder on the core side, in which thelayer (2) forming material is firstly injected, then the polyamide resincomposition is solely injected, and then finally the layer (2) formingmaterial is injected to fill the mold cavity, whereby the multilayerpreform having a five-layer structure (layer (2)/layer (1)/layer(2)/layer (1)/layer (2)) can be produced. The method for producing themultilayer preform is not limited to the aforementioned methods.

In the multilayer bottle, the thickness of the layer (2) is preferablyfrom 0.01 to 1.0 mm, and the thickness of the barrier layer (layer (1))is preferably from 0.005 to 0.2 mm (from 5 to 200 μm). The thickness ofthe multilayer bottle may not be constant over the entire bottle, and isgenerally in a range of from 0.2 to 1.0 mm.

The weight of the barrier layer in the multilayer bottle is preferablyfrom 1 to 20% by weight, more preferably from 2 to 15% by weight, andparticularly preferably from 3 to 10% by weight, based on the totalweight of the multilayer bottle. In the case where the weight of thebarrier layer is in the range, a multilayer bottle having favorable gasbarrier property can be obtained, and the multilayer preform as aprecursor can be easily molded into the multilayer bottle.

The bottom part of the multilayer bottle preferably has a petaloid shapeor a champagne shape.

In the multilayer bottle obtained by subjecting the multilayer preformto biaxially stretching blow molding, the gas barrier capability can beexhibited with the barrier layer that is present at least on the bodypart of the multilayer bottle, but higher gas barrier property can beobtained by extending the barrier layer to the vicinity of the end ofthe neck of the multilayer bottle. The stretching ratio on molding thepreform into the bottle is generally about from 9 to 13 times.

In the present invention, the multilayer bottle may be heat-set (heatsetting) in the blow molding die. The heat setting can be performedaccording to known conditions, and for example, the neck part of themultilayer preform is crystallized by infrared heating, and the heatsetting can be performed at a temperature of the mold of preferably from130 to 180° C., and more preferably from 145 to 165° C., for a period ofpreferably from 1 to 20 seconds, and more preferably from 3 to 10seconds.

EXAMPLE

The present invention will be described in more detail with reference toexamples and comparative examples below, but the present invention isnot limited to the examples. The measurements in the examples wereperformed in the following manners.

(1) Relative Viscosity of Polyamide

1 g of a polyamide was precisely weighed and dissolved in 100 mL of 96%sulfuric acid at 20 to 30° C. under stirring. After completelydissolved, 5 mL of the solution was quickly placed in a Cannon-Fenskeviscometer, and after placing in a thermostat chamber at 25° C. for 10minutes, the drop time (t) was measured. 96% sulfuric acid itself wasmeasured for the drop time (t0) in the same manner. The relativeviscosity was calculated from t and t0 according to the followingequation.

Relative viscosity=t/t0

(2) b* Value of Polyamide Pellets

The b* value was measured by a reflection method according to JIS K7105.A larger b* value means higher yellowness. As a measuring apparatus ofthe b* value, a color difference measuring apparatus (Model Z-E80 ColorMeasuring System), produced by Nippon Denshoku Industries Co., Ltd., wasused.

(3) Gas Barrier Property

A film was measured for oxygen transmission rate and oxygen transmissioncoefficient according to ASTM D3985 under an atmosphere of 23° C. and80% RH. The measurement was performed with OX-TRAN 2/16, produced byModern Controls, Inc. A lower value means better gas barrier property. Abottle was measured for oxygen transmission rate according to ASTM D3985under an atmosphere of 100% RH inside the bottle and 50% outside thebottle. The measurement was performed with OX-IRAN 2/16, produced byModern Controls, Inc. A lower value means better gas barrier property.

(4) Productivity and Molding Processability

A multilayer preform or a multilayer film was produced with the resincomposition as a barrier layer, and the number of bubbles formed in thebarrier layer was measured to evaluate productivity and moldingprocessability.

(5) Transparency

The barrier layer taken out from the multilayer preform was measured forhaze according to JIS K7105 and ASTM D1003 with a haze value measuringapparatus (Model COH-300A), produced by Nippon Denshoku Industries Co.,Ltd.

(6) Melt Viscosity of Polyamide

The melt viscosity was measured with Capilograph 1-D, produced by ToyoSeiki Seisaku-Sho, Ltd. by setting a capillary having a diameter or 1 mmand a length of 10 mm under conditions of 260° C. and a melt retentiontime of from 5 to 15 minutes.

Example 1 Melt Polymerization of Polyamide

15,000 g (102.6 mol) of precisely weighed adipic acid, 5.174 g (0.0488mol) of sodium hypophosphite and 2.803 g (0.0342 mol) of sodium acetatewere placed in a reaction vessel having an inner capacity of 50 Lequipped with a stirrer, a partial condenser, a total condenser, athermometer, a dropping funnel, a nitrogen introducing tube and stranddie, and after sufficiently replaced with nitrogen, the contents wereheated to 170° C. under stirring the system under a small amount ofnitrogen stream. 13,974 g (102.6 mol) of m-xylylenediamine was addeddropwise thereto under stirring, and the system was continuouslyincreased in temperature while removing generated condensation wateroutside the system. After completing the dropwise addition ofm-xylylenediamine, the inner temperature was set at 260° C., and thereaction was continued for 40 minutes. Thereafter, the system waspressurized with nitrogen, and the polymer was taken out through thestrand die and formed into pellets, so as to provide about 24 kg of apolyamide.

Solid Phase Polymerization of Polyamide

Subsequently, the polyamide was charged in a tumbling dryer having ajacket equipped with a nitrogen introducing tube, a vacuum line, avacuum pump and a thermocouple for measuring the inner temperature, andafter sufficiently replacing the interior of the tumbling dryer withnitrogen having a purity of 99% by volume or more while rotating at aconstant speed, the tumbling dryer was heated under the same nitrogenstream to heat the pellets to a temperature of 150° C. over about 150minutes. The pressure in the system, at which the temperature of thepellets reached 150° C., was reduced to 1 torr or less. The temperaturewas further increased to heat the pellets to a temperature of 200° C.over about 70 minutes, and maintained at 200° C. for 30 minutes.Nitrogen of having a purity of 99% by volume or more was then introducedinto the system, and the tumbling dryer was cooled with rotationmaintained to provide a polyamide 1 having a relative viscosity of 2.6.The resulting polyamide 1 had a b* value of 1.1.

Preparation of Polyamide Resin Composition

3.9 g (0.0065 mol) of calcium stearate was then added to kg of thepolyamide 1, and mixed by stirring in a tumbler for 10 minutes toprovide a polyamide resin composition 1.

Production of Film

The polyamide resin composition 1 was extruded at a discharge rate of 3kg/h into a film form by using a uniaxial extruder of mm in diameter, afilm extruder having a head equipped with a 600-mesh filter and a T-die,a cooling roller, a fish-eye detector (Model GX70W), produced byMamiya-OP Co., Ltd., and a wind-up device equipped with a winding deviceand the like, and the winding speed was controlled to form a film havinga width of 15 cm and a thickness of 50μ. The film was fed between thecamera and the light source of the fish-eye detector, and while windingwith the wind-up apparatus, the number of fish-eyes (having acircle-equivalent diameter of 20 μl or more) in the film having a widthof 10 cm and a length of 50 m was counted at the time after lapsing 1hour from the start of extrusion, whereby the number of fish-eyes per 1m² was calculated. The extrusion operation was continued after countingfish-eyes, and the resin pressure at the head of the extruder wasobserved to confirm occurrence of change thereof. The coloration stateof the resulting film was visually observed. The results are shown inTables 1 to 3.

Example 2

The melt-polymerization and the solid phase polymerization wereperformed in the same manner as in Example 1 except that the amount ofsodium hypophosphite was 12.953 g (0.1220 mol), and the amount of sodiumacetate was 7.008 g (0.0854 mol) to provide a polyamide 2 having arelative viscosity of 2.6 and a b* value of −2.0. The period of timewhere the temperature of the pellets was maintained at 200° C. was 20minutes.

7.6 g (0.0126 mol) of calcium stearate was then added to 20 kg of thepolyamide 2, and mixed by stirring in a tumbler for 10 minutes toprovide a polyamide resin composition 2, which was observed for thenumber of fish-eyes, the change in resin pressure and coloration statein the same manner as in Example 1. The results are shown in Tables 1 to3.

Example 3

The melt-polymerization and the solid phase polymerization wereperformed in the same manner as in Example 1 except that the amount ofsodium hypophosphite was 17.247 g (0.1627 mol), and the amount of sodiumacetate was 9.344 g (0.1139 mol) to provide a polyamide 3 having arelative viscosity of 2.6 and a b* value of −3.7. The period of timewhere the temperature of the pellets was maintained at 200° C. was 20minutes.

11.8 g (0.0194 mol) of calcium stearate was then added to 20 kg of thepolyamide 3, and mixed by stirring in a tumbler for 10 minutes toprovide a polyamide resin composition 3, which was observed for thenumber of fish-eyes, the change in resin pressure and coloration statein the same manner as in Example 1. The results are shown in Tables 1 to3.

Example 4

The melt-polymerization and the solid phase polymerization wereperformed in the same manner as in Example 1 except that the amount ofsodium hypophosphite was 25.871 g (0.2441 mol), and the amount of sodiumacetate was 14.016 g (0.1709 mol) to provide a polyamide 4 having arelative viscosity of 2.6 and a b* value of −4.5. The period of timewhere the temperature of the pellets was maintained at 200° C. was 20minutes.

18.8 g (0.0310 mol) of calcium stearate was then added to 20 kg of thepolyamide 4, and mixed by stirring in a tumbler for 10 minutes toprovide a polyamide resin composition 4, which was observed for thenumber of fish-eyes, the change in resin pressure and coloration statein the same manner as in Example 1. The results are shown in Tables 1 to3.

Example 5

A polyamide resin composition 5 was obtained in the same manner as inExample 2 except that 3.5 g (0.0058 mol) of calcium stearate was addedto 20 kg of a polyamide (polyamide 5) obtained throughmelt-polymerization and solid phase polymerization in the same manner asin Example 2, and was observed for the number of fish-eyes, the changein resin pressure and coloration state in the same manner as inExample 1. The results are shown in Tables 1 to 3.

Example 6

A polyamide resin composition 6 was obtained in the same manner as inExample 2 except that 17.1 g (0.0281 mol) of calcium stearate was addedto 20 kg of a polyamide (polyamide 6) obtained throughmelt-polymerization and solid phase polymerization in the same manner asin Example 2, and was observed for the number of fish-eyes, the changein resin pressure and coloration state in the same manner as inExample 1. The results are shown in Tables 1 to 3.

Example 7

The melt-polymerization and the solid phase polymerization wereperformed in the same manner as in Example 3 except that the amount ofsodium acetate was 8.009 g (0.0976 mol) to provide a polyamide 7 havinga relative viscosity of 2.6 and a b* value of −3.8. The period of timewhere the temperature of the pellets was maintained at 200° C. was 18minutes.

A polyamide resin composition 7 was then obtained in the same manner asin Example 3, and was observed for the number of fish-eyes, the changein resin pressure and coloration state in the same manner as inExample 1. The results are shown in Tables 1 to 3.

Example 8

The melt-polymerization and the solid phase polymerization wereperformed in the same manner as in Example 3 except that the amount ofsodium acetate was 12.014 g (0.1465 mol) to provide a polyamide 8 havinga relative viscosity of 2.6 and a b* value of −3.6. The period of timewhere the temperature of the pellets was maintained at 200° C. was 27minutes.

A polyamide resin composition 8 was then obtained in the same manner asin Example 3, and was observed for the number of fish-eyes, the changein resin pressure and coloration state in the same manner as inExample 1. The results are shown in Tables 1 to 3.

Example 9

14,250 g (97.5 mol) of precisely weighed adipic acid, 850 g (5.1 mol) ofisophthalic acid, 8.624 g (0.0814 mol) of sodium hypophosphite and 4.004g (0.0488 mol) of sodium acetate were placed in a reaction vessel havingan inner capacity of 50 L equipped with a stirrer, a partial condenser,a total condenser, a thermometer, a dropping funnel, a nitrogenintroducing tube and a strand die, and after sufficiently replaced withnitrogen, the contents were heated to 170° C. under stirring the systemunder a small amount of nitrogen stream. 13,974 g (102.6 mol) ofm-xylylenediamine was added dropwise thereto under stirring, and thesystem was continuously increased in temperature while removinggenerated condensation water outside the system. After completing thedropwise addition of m-xylylenediamine, the inner temperature was set at260° C., and the reaction was continued for 40 minutes. Thereafter, thesystem was pressurized with nitrogen, and the polymer was taken outthrough the strand die and formed into pellets, so as to provide about24 kg of a polyamide.

Subsequently, the polyamide was charged in a tumbling dryer having ajacket equipped with a nitrogen introducing tube, a vacuum line, avacuum pump and a thermocouple for measuring the inner temperature, andafter sufficiently replacing the interior of the tumbling dryer withnitrogen having a purity of 99% by volume or more while rotating at aconstant speed, the tumbling dryer was heated under the same nitrogenstream to heat the pellets to a temperature of 150° C. over about 150minutes. The pressure in the system, at which the temperature of thepellets reached 150° C., was reduced to 1 torr or less. The temperaturewas further increased to heat the pellets to a temperature of 200° C.over about 70 minutes, and maintained at 200° C. for 30 minutes.Nitrogen of having a purity of 99% by volume or more was then introducedinto the system, and the tumbling dryer was cooled with rotationmaintained to provide a polyamide 9 having a relative viscosity of 2.6.The resulting polyamide 9 had a b* value of 0.2.

3.9 g (0.0065 mol) of calcium stearate was then added to 20 kg of thepolyamide 9, and mixed by stirring in a tumbler for 10 minutes toprovide a polyamide resin composition 9. It was then observed for thenumber of fish-eyes, the change in resin pressure and coloration statein the same manner as in Example 1. The results are shown in Tables 1 to3.

Example 10

The melt-polymerization and the solid phase polymerization wereperformed in the same manner as in Example 9 except that the amount ofsodium hypophosphite was 12.953 g (0.1220 mol), and the amount of sodiumacetate was 7.008 g (0.0854 mol) to provide a polyamide 10 having arelative viscosity of 2.6 and a b* value of −0.5. The period of timewhere the temperature of the pellets was maintained at 200° C. was 27minutes.

7.6 g (0.0126 mol) of calcium stearate was then added to 20 kg of thepolyamide 10, and mixed by stirring in a tumbler for 10 minutes toprovide a polyamide resin composition 10, which was observed for thenumber of fish-eyes, the change in resin pressure and coloration statein the same manner as in Example 1. The results are shown in Tables 1 to3.

Comparative Example 1

A film was produced in the same manner as in Example 1 except thatcalcium stearate was not added, and was observed for the number offish-eyes, the change in resin pressure and coloration state in the samemanner as in Example 1. The results are shown in Tables 1 to 3.

TABLE 1 Phosphorus atom Molar ratio to Na Molar ratio of concentrationhypophosphite polyamide forming in polyamide Na Ca monomers (ppm)acetate stearate Example 1 MXDA/AA = 100/100 60 0.70 0.16 Example 2MXDA/AA = 100/100 150 0.70 0.13 Example 3 MXDA/AA = 100/100 200 0.700.15 Example 4 MXDA/AA = 100/100 300 0.70 0.16 Example 5 MXDA/AA =100/100 150 0.70 0.06 Example 6 MXDA/AA = 100/100 150 0.70 0.29 Example7 MXDA/AA = 100/100 200 0.60 0.15 Example 8 MXDA/AA = 100/100 200 0.900.15 Example 9 MXDA/AA/IA = 100 0.60 0.10 100/95/5 Example 10 MXDA/AA/IA= 150 0.70 0.13 100/95/5 Comparative MXDA/AA = 100/100 60 0.70 0 Example1 MXDA: m-xylylenediamine AA: adipic acid IA: isophthalic acid

TABLE 2 Retention time at 200° C. on solid phase Relative polymerizationviscosity of b* value of (minute) polyamide polyamide Example 1 30 2.61.1 Example 2 20 2.6 −2.0 Example 3 20 2.6 −3.7 Example 4 20 2.6 −4.5Example 5 20 2.6 −2.0 Example 6 20 2.6 −2.0 Example 7 18 2.6 −3.8Example 8 27 2.6 −3.6 Example 9 30 2.6 0.2 Example 10 27 2.6 −0.5Comparative 30 2.6 1.1 Example 1

TABLE 3 Resin pressure upon production of film (MPa) Number ofImmediately fish-eyes after After 3 After 6 of film Coloration startinghours hours (per m²) of film Example 1 2.1 2.1 2.1 320 none Example 22.1 2.1 2.1 330 none Example 3 2.1 2.1 2.1 400 none Example 4 2.1 2.12.1 460 none Example 5 2.1 2.1 2.1 320 none Example 6 2.1 2.1 2.1 350none Example 7 2.1 2.1 2.1 470 none Example 8 2.1 2.1 2.1 490 noneExample 9 2.1 2.1 2.1 400 none Example 10 2.1 2.1 2.1 410 noneComparative 2.3 3.8 5.6 360 none Example 1

As shown in Examples 1 to 10, the polyamide resin compositions of thepresent invention suffered less coloration, contained small amounts ofgel causing fish-eyes, and were stable in resin pressure upon extruding.In Comparative Example 1 having no calcium stearate added, the filterwas clogged due to denaturation of sodium hypophosphite, and thetime-lapse increase of the resin pressure was observed.

Example 11

99.963% by weight of poly-m-xylyleleadipamide (MX Nylon S6007, producedby Mitsubishi Gas Chemical Co., Inc.) as the polyamide (X), 0.03% byweight of calcium stearate (produced by Kanto Chemical Co., Inc.) as thefatty acid metallic salt, and 0.007% by weight ofpolyoxyethylenesorbitan monolaurate (Nonion LT-221, produced by NOFCorporation, kinematic eddy viscosity: 330 mm²/s) as the additive (A)were dry-mixed with a tumbler for 15 minutes. A three-layer preform (27g) containing polyester (F) layer/barrier layer/polyester (F) layer withthe resulting resin composition as the barrier layer was produced byinjection molding under the following conditions. In the followingconditions, the temperature of the core side injection cylinder washigh, the rotation number of the core side screw was high, and thebackpressure of the core side screw was low, as compared to the ordinaryconditions, whereby air was liable to be entrained to form a largeamount of bubbles.

The preform was cooled and then subjected to biaxially stretching blowmolding under heating to provide a multilayer bottle. As the resinconstituting the polyester (F) layer, polyethylene terephthalate (1101,produced by Invista, Inc.) having an intrinsic viscosity of 0.80(measured with a mixed solvent of phenol/tetrachloroethylene=6/4 (volumeratio) at a measurement temperature of 30° C.) was used. The barrierlayer suffered less fluctuation in thickness and had a uniform finishline with no disorder to provide a preform having a stable quality withfavorable moldability. The weight of the barrier layer with respect tothe total weight of the resulting multilayer bottle was 10% by weight.The resulting bottle had an oxygen transmission rate of 0.009cc/bottle·day·atm, which showed favorable barrier property. Theevaluation results are shown in Table 4.

Shape of Three-Layer Preform

The total length was 88 mm, the outer diameter was 20 mm, the thicknesswas 4.2 mm, and the weight was 21 g. The three-layer preform wasproduced with an injection molding machine, produced by Husky-Kortec(four pieces molded at one time). The screw used was an ordinary fullflight type.

Conditions of Molding Three-Layer Preform

Temperature of skin side injection cylinder: 285° C.Temperature of core side injection cylinder: 280° C.Temperature of resin path in mold: 280° C.Temperature of mold cooling water: 15° C.Rotation number of core side screw: 175 rpmBack pressure of core side screw: 0 psiCooling time: shown in Table 4

Shape of Multilayer Bottle

The total length was 155 mm, the outer diameter was 65 mm, the capacitywas 350 mL, the bottom shape was a champagne shape, and no dimple wasformed on the body part. The biaxially stretching blow molding wascarried out with a blow molding machine (Model EFB1000ET), produced byFrontier, Inc.

Conditions of Biaxially Stretching Blow Molding

Heating temperature of preform: 103° C.Pressure of stretching rod: 0.5 MPaPrimary blow pressure: 1.0 MPaSecondary blow pressure: 2.5 MPaPrimary blow delay time: 0.35 secPrimary blow time: 0.28 secSecondary blow time: 2.0 secBlow exhaust time: 0.6 secMold temperature: 30° C.

Example 12

99.95% by weight of polyamide containing a diamine component containingm-xylylenediamine and a dicarboxylic acid component containing 95% bymol of adipic acid and 5% by mol of isophthalic acid (melting point:233° C., half crystallization time: 59 s) as the polyamide (X), 0.04% byweight of calcium stearate (produced by Kanto Chemical Co., Inc.) as thefatty acid metallic salt, and 0.01% by weight of polyoxyethylenesorbitanmonolaurate (Nonion LT-221, produced by NOF Corporation, kinematic eddyviscosity: 330 mm²/s) as the additive (A) were dry-mixed with a tumblerfor 25 minutes. A multilayer bottle having the resulting resincomposition as a barrier layer was obtained in the same manner as inExample 11. The resulting bottle had an oxygen transmission rate of0.008 cc/bottle·day·atm, which showed favorable barrier property. Theevaluation results are shown in Table 4.

Example 13

99.98% by weight of polyamide containing a diamine component containingm-xylylenediamine and a dicarboxylic acid component containing 90% bymol of adipic acid and 10% by mol of isophthalic acid (melting point:226° C., half crystallization time: 133 s) as the polyamide (X), 0.015%by weight of calcium stearate (produced by Kanto Chemical Co., Inc.) asthe fatty acid metallic salt, and 0.005% by weight ofpolyoxyethylenesorbitan monolaurate (Nonion LT-221, produced by NOFCorporation, kinematic eddy viscosity: 330 mm²/s) as the additive (A)were dry-mixed with a tumbler for 20 minutes. A multilayer bottle havingthe resulting resin composition as a barrier layer was obtained in thesame manner as in Example 11. The resulting bottle had an oxygentransmission rate of 0.008 cc/bottle·day·atm, which showed favorablebarrier property. The evaluation results are shown in Table 4.

Comparative Example 2

99.98% by weight of poly-m-xylyleleadipamide (MX Nylon S6007, producedby Mitsubishi Gas Chemical Co., Inc.) as the polyamide (X) and 0.02% byweight of ethylenebisstearylamide (Alflow H-50, produced by NOFCorporation) as the additive (A) were dry-mixed with a tumbler for 5minutes. A multilayer bottle having the resulting resin composition as abarrier layer was obtained in the same manner as in Example 11.

The resulting bottle had an oxygen transmission rate of 0.009cc/bottle·day·atm. The evaluation results are shown in Table 4.

Comparative Example 3

99.985% by weight of poly-m-xylyleleadipamide (MX Nylon S6007, producedby Mitsubishi Gas Chemical Co., Inc.) as the polyamide (X) and 0.015% byweight of polyoxyethylenesorbitan monolaurate (Nonion LT-221, producedby NOF Corporation, kinematic eddy viscosity: 330 mm²/s) as the additive(A) were dry-mixed with a tumbler for 10 minutes. A multilayer bottlehaving the resulting resin composition as a barrier layer was obtainedin the same manner as in Example 11. The resulting bottle had an oxygentransmission rate of 0.009 cc/bottle·day·atm. The evaluation results areshown in Table 4.

Comparative Example 4

A multilayer bottle was obtained in the same manner as in Example 11except that the barrier layer was changed to poly-m-xylyleleadipamide(MX Nylon 56007, produced by Mitsubishi Gas Chemical Co., Inc.). Theevaluation results are shown in Table 4.

TABLE 4 Example Comparative Example 11 12 13 2 3 4 Polyamide (X) S6007IPA-5 IPA-10 S6007 S6007 S6007 Fatty acid metallic salt Ca-ST (ppm) 300400 150 0 0 0 Additive (A) EBS 0 0 0 200 0 0 LT-221 70 100 50 0 150 0Bubble forming 0 0 0 1.5 0.7 4.1 rate (%) Haze (%) 3 2 2 5 4 10 Coolingtime 4 3 2 6 5 6 (s) S6007: poly-m-xylyleleadipamide (MX Nylon S6007)IPA-5: 5 mol %-isophthalic acid-modified poly-m-xylyleleadipamideIPA-10: 10 mol %-isophthalic acid-modified poly-m-xylyleleadipamide EBS:ethylenebisstearylamide Ca-ST: calcium stearate LT-221:polyoxyethylenesorbitan monolaurate (Nonion LT-221)

Example 14

By using a multilayer film producing apparatus having two extruders, afeed block, a T-die, a cooling roller and a wind-up device, nylon 6(UBE1020B, a trade name, produced by Ube Industries, Ltd., which ishereinafter abbreviated as N6) and the resin composition obtained inExample 12 were co-extruded from the first extruder and the secondextruder, respectively, to produce a multilayer film having two speciesin three layers having a layer structure of N6 layer (10 μm)/barrierlayer (5 μm)/N6 layer (10 μm), to which an LLDPE film was then laminatedthereto to produce a multilayer film having three species in four layershaving a layer structure of LLDPE layer (20 μm)/N6 layer (10 μm)/barrierlayer (5 μm)/N6 layer (10 μm). As a screw for the barrier layer, a fullflight screw for polyolefin having a diameter (D) of 40 mm, L (screwlength)/D=24, a feed part length of 8D, a compression part length of 8D,a metering part of 8D and a compression ratio of 2.46 was used. Theoxygen transmission rate of the resulting film was 0.4 cc/m²·day·atm,which showed favorable barrier property. The barrier layer in the filmwas uniform with less fluctuation in thickness, and a film having stablequality without bubbles was obtained with good productivity andmoldability.

Example 15

A multilayer film was produced in the same manner as in Example 14except that a full flight screw for nylon having a diameter (D) of 40mm, L (screw length)/D=20, a feed part length of 8D, a compression partlength of 4D, a metering part of 8D and a compression ratio of 3.96 wasused as the screw for the barrier layer. The barrier layer in the filmwas uniform with less fluctuation in thickness, and a film having stablequality without bubbles was obtained with good productivity andmoldability.

Example 16

A multilayer film was produced in the same manner as in Example 14except that a double full flight screw having a diameter (D) of 40 mm, L(screw length)/D=25, a feed part length of 16D, a compression partlength of 5D, a metering part of 4D and a compression ratio of 2.67 wasused as the screw for the barrier layer. The barrier layer in the filmwas uniform with less fluctuation in thickness, and a film having stablequality without bubbles was obtained with good productivity andmoldability.

As shown in Examples 11 to 16, even under molding conditions where airwas liable to be entrained to form bubbles, the resin composition of thepresent invention can be formed into a molded article having goodcharacteristics without change of the molding conditions. Furthermore,it did not entrain air with screws having various shapes. Accordingly,the resin composition of the invention was considerably good inproductivity and moldability. It did not suffer whitening due tocrystallization immediately after molding, and excellent transparencywas obtained even with a short cooling time. It was also excellent ingas barrier property under a high humidity condition.

Example 17

A mixture of pellets containing 30% by weight of the polyamide resincomposition 1 (produced in Example 1) and 70% by weight of nylon 6(glade: 1030B, produced by Ube Industries, Ltd.) were agitated and mixedwith a tumbler. The mixture was melt-mixed at 260° C. with a uniaxialextruder having a diameter of 30 mm to produce mixed pellets 1. Themixed pellets 1 were dried under reduced pressure to control the watercontent to 0.03%, and then were measured for melt viscosity.

Example 18

A mixture of pellets containing 30% by weight of the polyamide resincomposition 2 (produced in Example 2) and 70% by weight of nylon 6(glade: 1030B, produced by Ube Industries, Ltd.) were agitated and mixedwith a tumbler. The mixture was melt-mixed at 260° C. with a uniaxialextruder having a diameter of 30 mm to produce mixed pellets 2. Themixed pellets 2 were dried under reduced pressure to control the watercontent to 0.03%, and then were measured for melt viscosity.

Comparative Example 5

A mixture of pellets containing 30% by weight of the polyamide 1(produced in Example 1, containing no calcium stearate) and 70% byweight of nylon 6 (glade: 1030B, produced by Ube Industries, Ltd.) wereagitated and mixed with a tumbler. The mixture was melt-mixed at 260° C.with a uniaxial extruder having a diameter of 30 mm to produce mixedpellets. The mixed pellets were dried under reduced pressure to controlthe water content to 0.03%, and then were measured for melt viscosity.

TABLE 5 Melt viscosity (Pa · s)/ shear rate: 100 sec⁻¹ Melt retentiontime 5 minutes 10 minutes Nylon 6 1,550 1,550 Polyamide 1 710 700Polyamide 2 700 690

TABLE 6 Melt viscosity (Pa · s)/ shear rate: 100 sec⁻¹ 5 minutes* 10minutes* Example 17 Arithmetic average value (a) 1,298 1,295 Actualmeasurement value (b) 1,340 1,330 (b)/(a) 1.03 1.03 Example 18Arithmetic average value (a) 1,295 1,292 Actual measurement value (b)1,330 1,360 (b)/(a) 1.03 1.05 Comparative Example 5 Arithmetic averagevalue (a) 1,298 1,295 Actual measurement value (b) 1,580 1,720 (b)/(a)1.22 1.33 *melt retention time

INDUSTRIAL APPLICABILITY

The polyamide resin composition of the present invention suffers lessbubbling upon molding irrespective of molding conditions including screwshape, temperature, back pressure and the like, and can be applied tocontinuous molding process for a prolonged period of time to provideexcellent productivity. A molded article suffering less coloration andgelation and is excellent in transparency and barrier property under ahigh humidity can be obtained irrespective of molding conditionsincluding temperature, cooling time and the like. A multilayer structurecontaining the polyamide resin composition of the present invention isfavorably applied to a package of foods, beverages, electronic parts andthe like, and the present invention provides considerably highindustrial value.

1. A polyamide resin composition comprising: a resin componentcontaining a polyamide (X) obtained through melt polycondensation of adiamine component containing 70% by mol or more of m-xylylenediamine anda dicarboxylic acid component containing 70% by mol or more of anα,ω-linear aliphatic dicarboxylic acid, a fatty acid metallic salthaving from 10 to 50 carbon atoms, and an additive (A), wherein theadditive (A) is at least one compound selected from the group consistingof a diamide compound obtained from a fatty acid having from 8 to 30carbon atoms and a diamine having from 2 to 10 carbon atoms, a diestercompound obtained from a fatty acid having from 8 to 30 carbon atoms anda diol having from 2 to 10 carbon atoms, and a surfactant.
 2. Thepolyamide resin composition as claimed in claim 1, wherein the polyamide(X) is a polyamide obtained through polycondensation of a diaminecomponent containing 70% by mol or more of m-xylylenediamine and adicarboxylic acid component containing 70% by mol or more of anα,ω-linear aliphatic dicarboxylic acid having from 4 to 20 carbon atomsand from 1 to 20% by mol of isophthalic acid.
 3. The polyamide resincomposition as claimed in claim 1, wherein the composition comprises thesurfactant, which is a nonionic surfactant having a kinematic eddyviscosity of 200 to 1,000 mm²/s at 25° C.
 4. The polyamide resincomposition as claimed in claim 1, wherein said fatty acid metallic saltis calcium stearate.
 5. The polyamide resin composition as claimed inclaim 1, wherein said fatty acid metallic salt is included in thepolyamide resin composition in an amount of 50 to 5,000 ppm.
 6. Thepolyamide resin composition as claimed in claim 1, wherein the polyamide(X) has been obtained through said melt polycondensation, in thepresence of a phosphorus atom-containing compound.
 7. The polyamideresin composition as claimed in claim 1, wherein said meltpolycondensation has been conducted in the presence of both a phosphorusatom-containing compound and an alkali metal compound.
 8. A multilayerstructure comprising a barrier layer comprising the resin composition asclaimed in claim
 1. 9. The multilayer structure as claimed in claim 8,wherein the structure further comprises a layer mainly comprising apolyester.
 10. The multilayer structure as claimed in claim 8, whereinthe structure further comprises a layer mainly comprising a polyolefin.11. The multilayer structure as claimed in claim 8, wherein thestructure further comprises a layer mainly comprising an aliphaticpolyamide.
 12. The multilayer structure as claimed in claim 9, whereinthe polyester is a thermoplastic polyester resin obtained throughpolymerization reaction of a dicarboxylic acid component containingterephthalic acid in an amount of 80% by mol or more, and a diolcomponent containing ethylene glycol in an amount of 80% by mol or more.13. The multilayer structure as claimed in claim 12, wherein thestructure is a multilayer bottle having a three-layer structureincluding polyester layer/barrier layer/polyester layer.
 14. Themultilayer structure as claimed in claim 12, wherein the structure is amultilayer bottle having a five-layer structure including polyesterlayer/barrier layer/polyester layer/barrier layer/polyester layer. 15.The multilayer structure as claimed in claim 8, wherein a weight of thebarrier layer is from 1 to 20% by weight based on the total weight ofthe multilayer structure.